Not one but at least four main things Ponyo:
The improbable and mythical nature of the Bible content and the absence of concrete evidence for it.
The repressive nature of the organisation and the stifling of personal growth in myself and other members.
The sudden realisation that the GB are planning on governing my life forever!
The theatricality of the role of the devil which I then extended to the case for God and realized that he too was a human fabrication as well.
What a beautiful relief it was to wake up to reality and shake off the JW shackles!